Cylindrical pressure vessels are commonly equipped with domed ends or heads. Such construction gives strength; it facilitates radiographic inspection of welds; and for vessels used in upright position, it provides for thorough emptying of liquid contents. When a vessel is so positioned, however, the space within one or both of the curved end portions may be unusable. Such a situation is encountered when a charge of solid material to be treated is placed in the vessel in an open-work container such as a wire basket for subsequent immersion in a liquid under pressure. The quantity of liquid or compressed gas required to fill the vessel and to be later recovered or discarded is then unnecessarily large.
The waste space could be filled by a hollow metal shape or a solid casting formed to occupy the end portion. The former would undergo great stress during pressure changes in the vessel and be subject to failure after prolonged use, if not initially. The latter would be costly to make and might be found to have internal voids. Concrete has been used, but it gives expansion problems and adds excessive weight.